You only had to see last night’s Mets lineup to have a good idea the team’s four-game winning streak to start the season was in serious jeopardy.

But surprisingly, the likes of Ronny Cedeno and Justin Turner weren’t as much the problem for the Mets as the rest of the lineup in a 6-2 loss to the Nationals at Citi Field.

Cedeno was 3-for-4 with an RBI and Turner delivered an RBI single on a night the rest of the Mets lineup accounted for only three hits. Lost was an opportunity for the Mets to tie a franchise record with a fifth straight victory to start the season.

It came on a night the Mets discovered they may lose David Wright for an extended period because of a small fracture at the middle joint of his right pinky. Cedeno replaced Wright in the starting lineup while Ike Davis and Josh Thole sat against Nationals lefty Ross Detwiler.

“With Ike not in there and David wasn’t in there, it changes some things, obviously,” manager Terry Collins said. “Against a guy like [Detwiler] your right-handed hitters have got to produce for you.”

The ugliness extended to defense, where Daniel Murphy and Lucas Duda had lapses as part of a three-run sixth inning for the Nationals.

Dillon Gee trailed only 1-0 heading into the sixth, but his night soon unraveled. Jayson Werth stroked an RBI single before Xavier Nady’s single put runners on the corners and ended Gee’s night. Roger Bernadina greeted Bobby Parnell with a grounder Murphy flubbed, allowing a run to score, before Wilson Ramos’ double — a ball Duda misjudged on the warning track in right — made it 4-0.

“If we make a couple of plays behind [Gee] he leaves here with an outstanding outing,” Collins said.

Gee’s final line included four runs allowed, three earned, on eight hits and one walk over 5 1/3 innings. The righty struck out six in a 104-pitch effort.

“I felt pretty good and I thought I threw the ball well,” Gee said.

The Mets didn’t score until the seventh, when Turner delivered an RBI single after Jason Bay had smacked a leadoff double. Cedeno’s RBI double in the eighth added another run.

Ian Desmond’s homer leading off the game was the only run for either team through five innings. Gee fell behind 2-0 in the count before leaving a fastball over the plate that Desmond hammered into the left-field seats.